Superabsorbent polymers (SAPs) are synthetic polymer materials having a capacity for absorbing 500 to 1000 times their own weight in moisture. Although developed for practical use in sanitary items, SAPs now find applications in a variety of fields including raw materials in soil conditioners for horticulture, water stopping agents for civil engineering and construction applications, sheets for raising seedlings, freshness preservatives for food distribution, goods for fomentation, and the like, in addition to sanitary items such as disposable diapers for children.
In the synthesis of SAPs, water plays various roles, for example, as a polymerization medium, and to facilitate the dispersion of a cross-linking agent upon surface cross-linking. In addition, serving as both an antistatic agent and a plasticizer for the polymer, residual water in the final product suppresses the formation of very small SAP dust and prevents the disintegration of SAP particles in applied processes. Given water, however, SAPs increase in stickiness on the resin surface, and undergo irreversible agglomeration between their particles. This viscosity increase and agglomeration brings about poor processability, such as a load increase, in the preparation and applied processes, which results in causing the SAPs to increase in particle size and to decrease in physical properties and productivity. Predominant among studies conducted thus far on SAPs are studies on polymerization processes and improvement in absorbency therethrough, and on surface cross-linking for increasing surface properties or ability to swell under pressure, together with studies on surface property change to improve permeability or to solve problems such as caking of SAPs during storage (anti-caking).
In this regard, Korean Application Patent Unexamined Publication No. 2012-0081113 discloses a method for producing an absorbent polymer containing water-insoluble inorganic particles. This technique, however, suffers from the disadvantage of inter-particular agglomeration and becoming poor in processability and productivity, as described above, because an increased water content on the surface of SAPs incurs an increase in surface viscosity. There is therefore a need for the development of SAPs that meet the conditions of both high water content and high processability.